Definition of a trough in the atmosphere
A trough is an extensive area with relatively low air pressure! surround by higher air pressure. We use the term trough primarily in connection with the flow at! high altitudes. Typically from 500 hPa and above.
The region of a trough is usually! represent by a wave-shap bulge that usually! extends over several hundr kilometers.
A trough contains an increasing cyclonic curvature! in the direction of flow up to the trough axis and a decreasing one after the trough axis! In the northern hemisphere, cyclonic means a flow that is curv to the left (counterclockwise).
If the wave-shap bulge in the upper! air flow is anticyclonic (i.e. curv to the right), then we speak of a ridge (high pressure).
Idealiz representation of the flow
at 500 hPa with a sequence of ridges and troughs. The arrows indicate the direction of the flow, the area with «+» the region of increasing cyclonic curvature, the area with «-» the decreasing cyclonic curvature in the trough.
Idealiz representation of the flow at 500 hPa with a sequence of ridges and troughs. The arrows indicate the direction of the flow, the area with “+” the region of increasing cyclonic curvature, the area with “-” the decreasing cyclonic curvature in the trough. (Source: MeteoSwiss)
Formation of a trough and its processes
The following explanations refer to the northern uae phone number library hemisphere, i.e. to our latitudes. It usually starts with a disturbance in the upper air flow, where warm subtropical air flows northwards first, follow by cold air of polar origin flowing southwards behind it. As the waves progress, a ridge forms in the warm area (anticyclonic curvature) and a trough in the cold area (cyclonic curvature). Several such combinations of troughs and ridges around the hemisphere are also call “Rossby waves”.
Schematic representation of the formation
of ridges and troughs up to the cut-off process (left) and the effects on the vertical processes (right).
Schematic representation of the formation of the fear could concern the reliability of your company ridges and troughs up to the “cut-off” process (left) and the effects on the vertical processes (right). (Source:
Sometimes it also happens that the cold polar air detaches itself alb directory from the southerly flow. This is known as a “cut-off” process, in which the clos high-altitude low develops its own dynamics and no longer moves with the precing high-altitude flow.
The formation of a trough has corresponding effects on the air layers below. Upstream, the “left curvature” and thus the cyclonic rotation increases. The result is a stretching of the air column, which lifts the air. This is why we often speak of the air mass being lift on the “front of the trough”. This lifting ultimately causes the air to cool and condense (precipitation) and at the same time a drop in pressure on the ground (formation of a low-altitude low). Exactly the opposite (warming and drying) happens downstream, behind the trough axis.
